The present invention relates to fluid displacement apparatus and more particularly to an improved scroll-type machine especially adapted for compressing gaseous fluids and having modified scroll means to provide increased speed of operation, improved efficiency, and a more compact design thus improving overall manufacturability of the apparatus.
A class of machines exists in the art generally known as "scroll" apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc. The present invention, however, while useful in basic design as a pump, is particularly applicable to compressors, and therefore for purposes of illustration is disclosed in the form of a gaseous fluid compressor.
Generally speaking, a conventional scroll apparatus comprises two spiral scroll wraps of symmetrical configuration each mounted on a separate parallel end or base plate to define a scroll member. In known scroll-type machines, the two scroll members are interfitted together with the wraps of one of the scroll members being rotationally displaced 180 degrees from the other. The apparatus generally operates by orbiting one scroll member (the "orbiting scroll") with respect to the other scroll member (the "fixed scroll") to create moving line contacts between the flanks of the respective wraps and define moving isolated crescent-shaped pockets or chambers of fluid. In practice, the orbiting scroll may be driven by the drive shaft, i.e. crank, or caused to orbit through the use of any other suitable known drive mechanism means. It is also known to rotate both scroll members with respect to one another as disclosed in U.S. Pat. No. 4,178,143.
The scroll members of the conventional scroll apparatus have spiral profiles which are commonly formed as involutes of a circle or other suitable geometric figure, and there is typically no relative rotation between the symmtrical scroll members during operation, i.e., the motion is purely curvilinear translation. The two scrolls are maintained in such substantially fixed angular relationship with respect to one another by an oldham coupling or the like, or are allowed to undergo some minimal rotation with resect to one another through utilization of an anti-rotational link (as shown and described in U.S. Pat. No. 4,609,334, filed Mar. 3, 1983 for Scroll-Type Machine). The fluid pockets carry the fluid to be handled from a first zone in the conventional scroll apparatus where a fluid inlet is provided, to a second zone in the center of the apparatus where a normally open fluid outlet or discharge port is provided. The volume of a sealed pocket progressively changes as it moves from the first zone to the second zone (in a compressor the sealed pockets progressively decrease in volume). Typically, there will be at least one pair of opposed symmetrical sealed pockets, and when the scroll members each comprise multiple wraps, as in a conventional scroll apparatus for compressing fluids there are several pairs of opposed symmetrical sealed pockets at any one instant in time, each pair having a different volume. In a compressor the second zone is at a higher pressure than the first zone and is physically located centrally in the apparatus, the first zone being located at the outer periphery of the apparatus.
Generally, the greater the arcuate length of a scroll wrap of constant thickness, the greater the total possible reduction in the volume of a fluid pocket as it moves to the second zone, i.e., the greater the possible volume ratio.
Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces of the wraps caused by radial forces of the orbiting scroll mass ("flank sealing"), and area contacts between the plane edge surfaces (the "tips") of each wrap and the opposite end plate ("tip sealing") caused by axial forces. For high efficiency, good sealing must be achieved for both types of contacts. In a conventional scroll compressor, good flank sealing is crucial, but at the same time, the friction associated with flank sealing can have detrimental wear effects.
The concept of a scroll-type apparatus has been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency and also are relatively small and lightweight for a given capacity. They tend to be somewhat quieter and more vibration free than many other types of compressors because they do not use large reciprocating parts (i.e. pistons, connecting rods, etc.), and because all fluid flow is monotonic with simultaneous compression in plural opposed pockets. Such machines also tend to have high reliability and durability because of the relative few moving parts utilized, the relatively low velocity of movement between the scrolls, and a inherent forgiveness to fluid contamination.
A conventional scroll compressor is a positive displacement fixed volume-ratio machine; at the suction inlet a given volume of a gaseous fluid is conventionally sealed off into the pair of opposed symmetrical pockets and compressed to a final volume at which point the pair of opposed pockets opens to a constantly open discharge port and the gaseous fluid is discharged. Because the conventional scroll compressor has a fixed volume ratio, it also has a fixed pressure ratio. The pressure of the final compressed volume just prior to discharge, and for that matter all intermediate volumes between initial seal-off and the final compressed volume just prior to discharge, is determined substantially by two factors: (1) the pressure of the initial suction volume at seal-off, and (2) the volume reduction during compression. Thus, the pressure of the initial charge will rise to whatever pressure is dictated by the volume reduction during compression. A three to one volume reduction machine, for example, will increase the pressure of the gas at discharge substantially more than threefold (due in part to quasi-adiabatic processes) over the inlet pressure no matter what the load pressure requirements are.
In a scroll compressor utilizing a normally open discharge port, discharge of the compressed fluid occurs as soon as either or both of a pair of fluid pockets are exposed to the discharge port. For conventional scroll apparatus to achieve desirable levels of volume reduction and pressure increase, however, scrolls with multiple wraps are required, thus making the diameter of each scroll member, and hence the overall size of the apparatus, relatively large. The relatively large size of the conventional scroll apparatus translates into high material and manufacturing cost; the multiple wraps of conventional scrolls themselves requiring intricate machining to fabricate.
It is therefore an object of this invention to provide a scroll apparatus having scroll members with a minimum number of scroll wraps that effect sealing of one or more fluid pockets and yet achieve the volume reduction of conventional scroll compressors.
It is a further object of this invention to provide a scroll compressor apparatus that comprises scroll members of aproximately a single wrap, thus resulting in greatly reduced scroll member diameter and allowing the apparatus to be a compact structure design, thereby improving the overall manufacturability and cost of the apparatus.
A further object of the invention resides in the provision of a scroll compressor apparatus having modified inner wrap ends that effect continued flank sealing until a single flank separation point is reached.
A further object of the invention resides in the provision of a discharge valve that enables the apparatus to take a fluid at inlet suction pressure and discharge it at design pressure in substantially a single crank revolution.
A still further object of the invention resides in the provision of a scroll compressor apparatus utilizing a discharge port valve that controls the volume ratio and enables the apparatus to achieve much greater pressure ratio versatility than prior known scroll compressors.
It is a still further object of the invention to provide a scroll compressor apparatus having a greater duration of discharge than comparable reciprocating or rotary piston compressors.
Additional objects and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.